linux-kernel - Re: [PATCH 1/5] ARM: DT: tegra114: add APB DMA controller DT entry

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Date:	Fri, 8 Mar 2013 23:36:00 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>
Subject: Re: [PATCH 1/5] ARM: DT: tegra114: add APB DMA controller DT entry

On Friday 08 March 2013 11:21 PM, Stephen Warren wrote:
> On 03/08/2013 06:52 AM, Laxman Dewangan wrote:
>> NVIDIA's Tegra114 has 32 channels APB DMA controller. Add DT entry for
>> APB DMA controllers and make it compatible with "nvidia,tegra114-apbdma".
>> diff --git a/arch/arm/boot/dts/tegra114.dtsi b/arch/arm/boot/dts/tegra114.dtsi
>> +	apbdma: dma {
>> +		compatible = "nvidia,tegra114-apbdma";
> So I know that the Tegra114 HW has a new channel-pause feature, which
> the driver /can/ use. However, if the driver didn't know about that
> feature, and continued to use the global-pause feature, would it still
> work fine?
>
> In other words, is the Tegra114 HW 100% backwards-compatible with the
> Tegra30 HW, it's just that there are new features that SW could
> optionally use?
>
> If that is true, then we should also include "nvidia,tegra30-apbdma" in
> the compatible value.

Tegra114 HW is not compatible with the tegra30 as with global pause, it 
is not able to write into the dma register in T114. On t114, the dma 
register is clock gated with global enable/disable.



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